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Re: RFC: PCI devices passthrough on Arm design proposal

On 17/07/2020 14:22, Bertrand Marquis wrote:
# Emulated PCI device tree node in libxl:

Libxl is creating a virtual PCI device tree node in the device tree
to enable the guest OS to discover the virtual PCI during guest
boot. We introduced the new config option [vpci="pci_ecam"] for
guests. When this config option is enabled in a guest configuration,
a PCI device tree node will be created in the guest device tree.

A new area has been reserved in the arm guest physical map at which
the VPCI bus is declared in the device tree (reg and ranges
parameters of the node). A trap handler for the PCI ECAM access from
guest has been registered at the defined address and redirects
requests to the VPCI driver in Xen.

Can't you deduce the requirement of such DT node based on the presence
of a 'pci=' option in the same config file?

Also I wouldn't discard that in the future you might want to use
different emulators for different devices, so it might be helpful to
introduce something like:

pci = [ '08:00.0,backend=vpci', '09:00.0,backend=xenpt', 
'0a:00.0,backend=qemu', ... ]

I like this idea :).

For the time being Arm will require backend=vpci for all the passed
through devices, but I wouldn't rule out this changing in the future.

We need it for the case where no device is declared in the config file and the 
wants to add devices using xl later. In this case we must have the DT node for 
to work.

Are you suggesting that you plan to implement PCI hotplug?


Julien Grall



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